This invention relates to a thermoplastic resin composition having a good moldability and also well balanced between heat resistance and high-impact properties.
It has been well known that .alpha.-methylstyrene-acrylonitrile copolymers are generally blended with ABS resins to improve the heat resistance of ABS resins (e.g., see Japanese Patent Application laid-open No. Sho 58-117241/1983).
However, .alpha.-methylstyrene-acrylonitrile copolymers have a high thermal deformation temperature and nevertheless has a high melt viscosity; thus thermoplastic resin compositions consisting of such copolymers and ABS resins and having good heat resistance have a far lowered moldability as compared with that of general ABS resins. For improving the moldability of conventional thermoplastic resins hving a good heat resistance, it is effective to reduce the molecular weight of .alpha.-methylstyrene-acrylonitrile copolymers, but their high-impact properties and heat resistance lower exponentially. Further, in the case of addition of lubricants, too, their moldability and high impact properties are enhanced, but their heat resistance lowers. Thus, in the design of thermoplastic resin compositions having a good heat resistance, it has been the most important problem to balance the three factors of heat stability, moldability and high-impact properties.